Device comprising a multilayer structure and rollers

ABSTRACT

The invention relates to a device comprising a multilayered structure with a first portion and a second portion wherein the first portion is conceived to be rolled about a first roller, said device comprising a second roller for receiving the second portion for at least partially counteracting the effects of mechanical strain induced in the multilayered structure upon said rolling. The first roller is rotated in a first direction, whereby the second roller is rotated in a second direction. Preferably, the diameters of the first roller and the second roller are equal. Alternatively, the edge portions A, B of the multilayer structure are suitably interconnected by stoppers for preventing creeping.

FIELD OF THE INVENTION

The invention relates to a device comprising a multilayer structure witha first portion and a second portion wherein the first portion isconceived to be wound about a first roller.

BACKGROUND OF THE INVENTION

An example of a device as is set forth in the opening paragraph relatesto an electronic apparatus comprising a flexible, notably rollabledisplay. Rollable displays consist of several layers of suitablematerials laminated on top of each other. When bending or rolling such alayer stack, creep and/or buckles can arise due to length differencesbetween layers on the inside and outside of the curvature. Thisphenomenon appears particularly when, as shown in FIG. 1 (“creep”), anedge portion of the multilayer 3 is being held stationary with respectto a point of attachment to a part 7 of the device.

Creep and resulting misalignment between an upper and lower laminate canalso occur when a stack of two laminates is bent. The laminate at theinside of the curvature needs less length and will therefore extendbeyond the edge of the outer laminate. Buckling (local delaminationdefects) can occur when the same laminate stack, this time beingstationary arranged at both ends with respect to some parts 8, 9 of thedevice, is bent (see, FIG. 1 “buckling”). Now the superfluous length ofthe inner laminate causes a buckle that compensates for the lengthdifference. These phenomena will be discussed in more detail withreference to FIG. 1.

It is a disadvantage of a known device that the durability and/orfunctionality of the multilayer structure are reduced due to damages tothe multilayer structure as a consequence of creeping and/or buckling.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a device as is set forth inthe opening paragraph wherein reliability of the device is improved.

To this end the device according to the invention comprises a secondroller for receiving a second portion for at least partiallycounteracting the effects of mechanical strain induced in the multilayerstructure upon said winding.

The technical measure of the invention is based on the insight that byapplying different rolling strategies, creep and/or buckling problemscan be minimized. The multilayer structure comprises a suitable numberof material layers laminated on top of each other. For example, in caseswhen the multilayer structure comprises a display, the multilayerstructure may comprise a flexible layer, notably an electrophoreticmaterial, a binder, an adhesive sandwiched between two plasticsubstrates, for example of 25 micrometers each. Applying proper rollingstrategies can increase durability of the device due to the fact thatcreep, either in the roll direction or perpendicular to the rolldirection, is substantially minimized leading to improved reliability ofthe device when the multilayer structure is repetitively rolled up andunrolled, or kept rolled-up for a prolonged time. In addition, therespective alignment of the layers forming the multilayer structure isnot altered during rolling up and unrolling improving the performance ofthe device as a whole. In other words the first roller supporting thefirst portion of the multilayer structure wound thereon and the secondroller supporting a second portion of the multilayer structure woundthereon mechanically cooperate with each other. This feature isparticularly advantageous for flexible displays, for example displayscomprising a material having electrophoretic principles. Alternativelyor additionally, this feature is advantageous for flexible colordisplays having a filter which substantially may not be displaced withinthe multilayer structure with respect to other structures. Arollable/flexible color display has a display effect layer, reflectingor emitting white light, combined with a color filter layer. Coloredsub-pixels of the display are arranged into rows or columns in a roll-updirection. Suitable embodiments of the flexible color displays arediscussed with reference to FIGS. 7-11.

Preferably, the rollers are arranged to roll the multilayer structurewith the same surface facing in the same direction. In this case therollers will be rolling in the opposite directions as observed from theoutside. In a further embodiment the first roller and the second rollerare wound in the same direction as observed from the outside. In thiscase the inward and outward surfaces on both rollers will be different.It is noted that the proposed rolling geometry is particularlybeneficial for electronic devices comprising flexible, notably rollabledisplays, in particular color displays because the color filter has tostay accurately aligned to a pixelated backplane.

In a further embodiment of the device according to the invention themultilayer structure extends freely along a path between the firstroller and the second roller, said path being selected to counteract netlongitudinal shifts between the layers forming the multilayer. Thisembodiment is found to be particularly suitable for counteracting netcreep. This feature will be discussed in more detail with reference toFIG. 5.

In a further embodiment of the device according to the invention thedevice comprises a multilayered structure with a first portioncomprising a first edge and a second portion comprising a second edgewherein the first portion is conceived to be rolled about a firstroller, whereby layers forming the multilayered structure are fixed atleast in the area of the first edge and the second edge.

This particular embodiment is easy to implement and provides simple andreliable means to counteract creeping thereby improving reliability ofthe device as a whole, as well as durability due to the fact that therespective layers forming the multilayer do not shift with respect toeach other during rolling and unrolling. Further advantageousembodiments are set forth in claims 10-17.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents a schematic illustration of creep and bucklingphenomena.

FIG. 2 presents a schematic illustration of strain in a bent multilayerstructure.

FIG. 3 presents a schematic view of an embodiment of the deviceaccording to the invention.

FIG. 4 presents a schematic view of a further embodiment of the deviceaccording to the invention.

FIG. 5 presents a schematic view of a detail of an embodiment of thedevice of FIG. 4.

FIG. 6 presents a schematic view of an embodiment of a device accordingto the invention.

FIG. 7 presents a schematic view of an embodiment of a multilayerstructure for use in the device according to the invention.

FIG. 8 presents a schematic view of a further embodiment of a multilayerstructure for use in the device according to the invention.

FIG. 9 presents a schematic view of a further embodiment of a multilayerstructure for use in the device according to the invention.

FIG. 10 presents a schematic view of a further embodiment of amultilayer structure for use in the device according to the invention.

FIG. 11 presents a schematic view of a further embodiment of amultilayer structure for use in the device according to the invention.

DETAILED DESCRIPTION

FIG. 1 presents a schematic illustration 10 of creep and bucklingphenomena. These effects are illustrated using a multilayered structure2, 4 comprising two layers. It should be appreciated that thisembodiment is strictly illustrative, leaving the option open for using amultilayer structure with more than two layers. The layers 2 a, 2 b,respectively 4 a, 4 b are preferably laminated to each other; however,other adhesion or co-planarization principles are possible. It is alsonoted that also the left-hand side embodiment refers to the effect ofcreeping whereby two adjacent points 2 a, 2 b within a suitablemultilayer stack are displaced with respect to each other, see 3 a, 3 b,due to the relaxation of strain upon bending 3. Creep phenomenon isparticularly pronounced for a multilayer wherein the layers are fixed toeach other at an extremity, for example when being kept in place bysuitable parts of the device 7, 8, and 9.

Buckling phenomenon is illustrated for a situation when layers are fixedto each other at both ends by suitable parts 8, 9 of the device. Forexample, a roller whereto the multilayer is attached can serve as suchpart. In addition a suitable grip portion (not shown) which is used tounroll the multilayer structure can be such a portion 9. Buckling (localdetachment defects) can occur when the same stack, notably a laminatedstack, fixed at both ends, is bent. Now the superfluous length of theinner laminate causes a buckle 6 that compensates for the lengthdifference. It is noted that the adjacent points 5 a, 5 b keep theirrelative positions.

FIG. 2 presents a schematic illustration of strain in a bent multilayerstructure. In this example an isotropic bar 20 is bent over a radius R.Internal strain, being tensile or compressive, is caused in accordancewith line 25. The inner layers 24, 23 are in a state of compressionwhich gradually transforms into a state of tension for the layers 22,21. The neutral plane 20N is defined as a line or a section of a planewherein no strain and no tension occurs. The strain profile isindependent of material properties of the layers and solely depends onthe bending radius and a displacement Ay in a transverse direction yacross the stack 20. For a laminate the plate comprises multiple layershaving different properties. This does not influence the strain profile;however, the position of the neutral line 20N is determined by thematerial properties. A significant compliant middle layer can result ina certain length at the end of the roll where the laminate rearrangesback to the original (undeformed) state with a zero strain profile.

FIG. 3 presents a schematic view of an embodiment of the deviceaccording to the invention. In accordance to the technical measure ofthe invention the device 35 comprises a first roller 38 and the secondroller 39 about which respective portions of the multilayer structure 35a are wound. The first roller 38 is rotated in a first direction,whereby the second roller 39 is rotated in an opposite direction. Thisresults in the outer surface 36 always being at the outer side of eachroller 38 and 39. Preferably, the diameters of the first roller 38 andthe second roller 39 are equal. This results in a substantial reductionof the effects of strain in respective portions of the multilayerstructure 35 a. The roller arrangement of FIG. 3 is suitable tocounteract the creeping phenomenon. It is noted that it is sufficient tosuitably interconnect layers at both edges A, B of the multilayerstructure for preventing creeping, like is shown in embodiment 30 ofFIG. 3. In this case the terminal portions comprise suitable stoppers 33a, 33 b arranged to prevent mutual displacement of the layers 31, 32during rolling. For example, the stoppers may be integrated in themultilayer structure. Embodiments of suitable stoppers comprise extrastrong lamination, fastening means, like pins, slots, clamps, glueseams, etc. This effect can be reached also by suitably rollingsubsequent layers of the multilayer structure on each other so that theindividual layers are being fixed to each other by application of therolling force.

It is preferable to use such stoppers in combination with the embodimentof the display 35, counteracting the effects of strain even moreeffectively. Preferably, such embodiment is combined with an embodimentdiscussed with reference to FIG. 4.

FIG. 4 presents a schematic view of a further embodiment of the deviceaccording to the invention. In this particular embodiment of the device40 according to the invention the first roller 43 is arranged to rotatein the same direction as the second roller 44. In this case the outerlayer 41 at the position of the first roller 43 becomes an inner layerat the position of the second roller 44. The rollers 43 and 44 arearranged to cause the potential creep shift being built up in a portionof the multilayer structure associated with the roller 44 to be in anopposite direction and, therefore, to counteract the potential creepshift being built up in the portion associated with the roller 43. Thishas an additional advantageous effect that the potential creep isdivided over the two rollers 43, 44. Preferably, for optimalcompensation of the creep shift, the rollers 43, 44 should be selectedof the same diameter. Alternatively, they may be of different diameter,provided a number of revolutions of the multilayer structure on a rollerwith a smaller diameter is smaller. This is explained by the fact thecreep shift is proportional to an increment of the path an externallayer has to travel upon bending. Due to this arrangement of theroller's geometry also buckling effects are counteracted.

FIG. 5 presents a schematic view of a further embodiment of the deviceaccording to the invention. Hereby a portion of the multilayer structure50 comprising layers 51 a, 51 b, respectively 52 a, 52 b is shown, saidportion being positioned between terminal portions 51, 52 being woundaround respective rollers (not shown). In the case of creep, the lengthdifferences at positions A and B in FIG. 5, caused by the relief ofstrain in the rolled portion, are assumed to be capable of driving thecreep all the way through the unsupported multilayer, notably a film,without the strain which is present in the rolled part of laminate. Thisdepends on the material properties, bending radius and the length of thefreestanding part L. In addition the laminate must creep between thesame layers in order to have matching profiles. Provided with theassumption that the laminate will creep as depicted in FIG. 5, thesolution of FIG. 4 will have an effect of buckle prevention in thefreestanding part and the rolled up portions. When the geometry of therollers is suitably selected the creep areas A and B in the portion Lare accurately compensated in net terms relieving the overall strain inthe multilayer structure 50. It is noted that substantially the sameamount of creep (measured in length) is induced in opposite directionsin both halves of the multilayer structure, notably a flexible displayor the like. Therefore, the totally relaxed rolled-up state has no netlength difference between the top and the bottom part of the multilayerstructure. This creates the possibility to add end stoppers at bothsides.

FIG. 6 presents a schematic view of an embodiment of a device 60according to the invention. The device 60 preferably relates to anelectronic device such as a portable telephone, a palmtop computer orany other hand operated device comprising a collapsible, notably aflexible display. The electronic device 60 in this case comprises afirst portion of a housing 61 and a second portion of a housing 62, saidportions of the housing being displaceable with respect to each other torespective positions 61′, 62′. The flexible display 63 is wound aboutthe first roller 61 a and the second roller 62 a for compensating therelaxation effects of the internal strain caused by the rollers 61 a, 62a. Although this embodiment is described with reference to the rollersarranged to rotate in the same direction, it will be appreciated thatany embodiment discussed with reference to FIG. 3 is applicable.

FIG. 7 presents a schematic view of a multilayer structure for use inthe device according to the invention. In this example a cross-sectionalview of a conformable, flexible or roll up display 100 is shown inaccordance with principles of one embodiment. A display effect layer 128includes materials for the transmission and dispersion of light. In theembodiment of FIG. 7, the display effect layer 128 may include liquidcrystal, an electrophoretic display medium or any other emitting orreflective material for guiding light to a viewer. A backplane substrate114 may include a flexible polymer material on which an active matrixlayer 115 is formed including sub-pixels 116 and other electroniccomponents. These electronic components may include transistors (thinfilm transistors TFT), capacitors, conductive lines, etc. For simplicityonly sub-pixels 116 are shown. For a back lit embodiment, light ispassed through substrate 114 or other back end device to provide lightthrough sub-pixels 116. Other embodiments may include reflectivedisplays where light is reflected from sub-pixels 116 from the viewingside of the sub-pixels 116. A cell gap 118 is filled with a displayeffect material, such as, e.g., liquid crystal, electrophoretic displaymedium (e.g., the capsules contain electrophoretic ink from themanufacturer E Ink Corporation) or other display effect material whichis responsive to pixels 116. For example, when activated the pixels 116cause orientation of the liquid crystal or a change in the E inkcapsules as is known in the art. A substrate 121 may include a commonelectrode 120 formed thereon. The common electrode 120 cooperates withthe sub-pixels 116 to orient or adjust the state of the adjacent displayeffect material. A color filter layer 152 is provided as part orsubstrate 121.

Referring to FIG. 8, a sub-pixel array 150 includes an arrangement ofsub-pixels 116 which are configured to be assigned same color values ina linear relationship, e.g., in same rows or columns 132, 134 and 136(referred to hereinafter as rows for ease of reference). Each row 132,134 and 136 corresponds to a same color. Colored sub-pixels 116 of thedisplay 100 are arranged into rows in a roll-up direction 140 (a roll142 is shown in this view for illustrative purposes). The three colorrows (e.g., Red 134, Green 136 and Blue 138) repeat across the display.While three color components are illustratively depicted and described,other arrangements may be provided. For example, in one embodiment, fourrow types may be employed (e.g., Red, Green, Blue and White (RGBW)).Each row (132, 134, and 136) is oriented in the roll up direction 140,which is transverse to a longitudinal axis of a spool or roll 142.

Referring to FIG. 9, the rollable color display 100 has the displayeffect layer 128 formed and a color filter layer 152 is to be placed inalignment with the sub-pixels 116 on an active/passive matrix layer 115.The color filter layer 152 may be fabricated and placed in a pluralityof different ways. The color filter layer 152 may be formed bydeposition and photolithographic patterning over the display effectlayer 128. For example, a first color is deposited followed by apatterning process which forms longitudinal stripes 154 of the firstcolor in the direction of the roll up 140. Each stripe 154 of the firstcolor corresponds to and is aligned in a direction transverse to theroll up direction 140. Similar processing is performed to define stripes154 for the other color filters corresponding to the sub-pixels 116 ofthat color. Color filters may include materials of between about 100 nmand about 10 microns in thickness and are preferably polymericmaterials, which may be known.

In alternate embodiments, a color filter layer 152 may be formed by spincoating, spray coating, evaporating, doctor blading or similardeposition methods. In one embodiment, the color filter layer is formedas a sheet having alternating color components as illustratively shownin FIG. 10. A color filter sheet 160 may be formed in a single sheethaving different colors 161-163 alternating thereon. Sheet 160 mayinclude a thin polymeric material fabricated in an extrusion process.Sheet 160 may be glued or otherwise adhered to the display 100 (FIG. 3)to provide color filter layer 152.

Advantageously, the color filter layer 152 need only be concerned abouta sub-pixel pitch in a direction transverse to the roll-up direction140. This makes alignment much easier between the sub-pixels 116 and thecolor filters. In the present disclosure, colored sub-pixels 116 arearranged in horizontal stripes. This can have implications on thearrangement of rows and columns on the display and thereby theperformance needed from driving or backplane electronics.

Referring to FIG. 11, color filter stripes 170 may be secured using afixing strip 172 along one of the edges perpendicular to the rollingdirection 140. The fixing strip 172 binds the display effect layer 128and color filter layer 152 along one of the non-rolling display edges.As described, brightness decreases and/or color errors caused byalignment problems during display bending or rolling are avoided bypatterning color filters into continuous stripes 170 which extend in theroll up direction 140. A radius difference between the display effectlayer 128 and the color filter layer 152 is substantially eliminatedsince misalignment between the color filters and the underlying pixelsis eliminated. No brightness decrease or color errors will occur.

FIG. 11 illustratively shows an RGB (red, green, blue) color display 200according to one embodiment. However, arrangements other than RGB, suchas RGBW RBG White) or CMY (Cyan, Magenta, Yellow) may be employed. Blackstripes (boot shown) may also be employed between the colored stripes170 to separate or delineate the stripes 170. It should be understoodthat pixels comprised of three sub-pixels are arranged together suchthat three adjacent rows cover the three sub-pixels needed for a pixelimage. The color filter stripes need not continuously alternate, e.g.,RGB; RGB, etc.; instead other arrangement are possible, e.g., RGB, BGR,RGB, so that the same colors in this case B and R can be formed adjacentto one another. This may ease tolerances and improve manufacturability.

Depending on the lamination glue properties of fixing strip 172, fixingstrip may be employed to fix the display effect layer 128 and colorfilter layer 152 along one of the non-rolling display edges to preventun-wanted drifting of the two layers with respect to each other. Fixingstrip 170 may be employed along one side of the display 200, and permitthe movement of color filter layer 152 relative to the display effectlayer without color errors due to bending or roll up. Other arrangementsare also possible, such as, e.g., employing one or more fixing spots 176at opposite sides of the display 200.

It should be noted that every embodiment of the flexible displaysdiscussed with reference to any of the FIGS. 7-11 may be rolled inaccording to the principles set-out in FIGS. 3, 4. Alternatively oradditionally the flexible displays discussed with reference to any ofthe FIGS. 7-11 may be provided with edge stoppers as discussed withreference to embodiment 30 of FIG. 3.

It will be appreciated that although specific embodiments of the deviceaccording to the invention are discussed separately for claritypurposes, interchangeability of compatible features discussed withreference to isolated figures is envisaged. While specific embodimentshave been described above, it will be appreciated that the invention maybe practiced otherwise than as described. The descriptions above areintended to be illustrative, not limiting. Thus, it will be apparent toone skilled in the art that modifications may be made to the inventionas described in the foregoing without departing from the scope of theclaims set out below.

1. An electronic device comprising: a flexible display having a firstportion and a second portion; a first roller; and a second roller;wherein the first portion is adapted for rolling about the first roller,the second portion is wound about the second roller, and the firstroller and the second roller are rotatable in opposite directions.
 2. Adevice according to claim 1, wherein a first portion comprises a firstedge and a second portion comprises a second edge, and wherein thelayers forming the multilayered structure are mechanicallyinterconnected at least in the area of the first edge and the secondedge.
 3. A device according to claim 1, wherein a diameter of the firstroller substantially equals a diameter of the second roller.
 4. A deviceaccording to claim 1, wherein the flexible display comprises a pluralityof rows, each row being oriented in a roll up direction, which istransverse to a longitudinal axis of a spool or roll.
 5. A deviceaccording to claim 4, wherein the display comprises electrophoreticmaterial.
 6. A device according to claim 4, said device beingaccommodated in a housing comprising a first portion and a secondportion, said first portion being displaceably arranged with respect tothe second portion, wherein the first roller is arranged in the firstportion and the second roller is arranged in the second portion.
 7. Adevice comprising a multilayered structure with a first portioncomprising a first edge and a second portion comprising a second edgewherein the first portion is adapted for rolling about a first rollerand the second portion is wound about a second roller, wherein layersforming the multilayered structure are mechanically interconnected atleast in the area of the first edge and the second edge, and wherein themultilayer structure comprises a flexible display and wherein the firstroller and the second roller are rotatable in opposite directions.
 8. Adevice according to claim 7, wherein a diameter of the first rollersubstantially equals a diameter of the second roller.
 9. A deviceaccording to claim 7, wherein the flexible display comprises a pluralityof rows, each row oriented in a roll up direction, which is transverseto a longitudinal axis of a spool or roll.
 10. A device according toclaim 9, wherein the display comprises electrophoretic material.
 11. Adevice according to claim 9, said device being accommodated in a housingcomprising a first portion and a second portion, said first portionbeing displaceably arranged with respect to the second portion, whereinthe first roller is arranged in the first portion and the second rolleris arranged in the second portion.
 12. A device according to claim 10,said device being accommodated in a housing comprising a first portionand a second portion, said first portion being displaceably arrangedwith respect to the second portion, wherein the first roller is arrangedin the first portion and the second roller is arranged in the secondportion.
 13. A device according to claim 1, wherein the multilayerstructure comprises a compliant middle layer for at least partiallycounteracting the effects of mechanical strain induced in themultilayered structure upon said rolling about the first roller.
 14. Adevice according to claim 5, said device being accommodated in a housingcomprising a first portion and a second portion, said first portionbeing displaceably arranged with respect to the second portion, whereinthe first roller is arranged in the first portion and the second rolleris arranged in the second portion.
 15. A device according to claim 7,wherein the multilayer structure comprises a compliant middle layer forat least partially counteracting the effects of mechanical straininduced in the multilayered structure upon said rolling about the firstroller.